fix: handle double host prefix when Netdata running in a podman container

[ilyam8]

Summary

Fixes: #12259

mountinfo_find_by_filesystem_super_option returns the path with /host in a podman container and without in a docker container.

$ podman exec nd cat /proc/self/mountinfo | grep cgroup
435 433 0:25 / /host/sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - cgroup2 cgroup2 rw
447 427 0:25 / /sys/fs/cgroup ro,nosuid,nodev,noexec,relatime - cgroup2 cgroup2 rw

$ docker exec nd cat /proc/self/mountinfo | grep cgroup
302 301 0:25 / /sys/fs/cgroup ro,nosuid,nodev,noexec,relatime - cgroup2 cgroup rw
307 305 0:25 / /host/sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - cgroup2 cgroup2 rw

Test Plan

• cgroup v1 enabled; run Netdata podman/docker container, ensure Netdata can discover other containers.
• cgroup v2 enabled; run Netdata podman/docker container, ensure Netdata can discover other containers.

Additional Information